Speed reduction mechanism and motor with speed reducer

1. A speed reduction mechanism comprising:

an eccentric shaft rotated around a rotation axis by a rotational force of a motor section and having an eccentric outer peripheral surface with a center at an eccentric position eccentric to the rotation axis;

a rocking gear rotatably supported by the eccentric outer peripheral surface via a first bearing and having first inner teeth and first outer teeth;

a fixed gear having second inner teeth which mesh with the first outer teeth of the rocking gear and which are concentric with the rotation axis; and

an output gear having second outer teeth which mesh with the first inner teeth of the rocking gear and which are concentric with the rotation axis,

wherein at least part of a range of meshing between the first outer teeth of the rocking gear and the second inner teeth of the fixed gear and at least part of a range of meshing between the first inner teeth of the rocking gear and the second outer teeth of the output gear overlap each other in a radial direction orthogonal to the rotation axis,

wherein a center position in a direction of the rotation axis of the range of meshing between the first outer teeth of the rocking gear and the second inner teeth of the fixed gear, a center position in the direction of the rotation axis of the range of meshing between the first inner teeth of the rocking gear and the second outer teeth of the output gear, and a center position in the direction of the rotation axis of the first bearing are located on a same plane in the radial direction.

2. The speed reduction mechanism according to claim 1 , wherein the rocking gear comprises:

a rocking gear body which is in a circular plate shape extending in the radial direction;

a bearing housing which is in a cylindrical shape standing upright from a radial-direction center of the rocking gear body and fitted to the first bearing; and

a tooth wall which is in a cylindrical shape standing upright from an outer peripheral section of the rocking gear body toward a same direction as an upright direction of the bearing housing,

wherein the first inner teeth are formed on an inner peripheral surface of the tooth wall, and

the first outer teeth are formed on an outer peripheral surface of the tooth wall.

3. The speed reduction mechanism according to claim 1 , further comprising:

a gear housing which rotatably supports the eccentric shaft and in which the rocking gear and the fixed gear are accommodated; and

a cover which is fixed to the gear housing and which rotatably supports the output gear via a second bearing,

wherein a first meshing position between the first outer teeth of the rocking gear and the second inner teeth of the fixed gear, a second meshing position between the first inner teeth of the rocking gear and the second outer teeth of the output gear, and the second bearing are disposed side by side in a direction of the rotation axis, and

a lubricant reservoir is provided between the first meshing position, the second meshing position, and the second bearing.

4. The speed reduction mechanism according to claim 3 , wherein

the second bearing is a rolling bearing having an inner ring and an outer ring,

the inner ring of the second bearing is fitted to the output gear so that one end of the inner ring contacts the output gear, and

the outer ring of the second bearing is fitted to the cover so that another end of the outer ring on an opposite side to the one end of the inner ring contacts the cover.

5. A motor with a speed reducer, comprising:

the speed reduction mechanism according to claim 1 ; and

the motor section having a rotation shaft connected to the eccentric shaft and rotating around the rotation axis.